Typically, the furnace walls are lined with water tubes, pipes through which water is circulated, heated and converted into steam and collected in a large drum usually above the furnace. In order to heat large quantities of water, multiple burner assemblies can be employed which are inserted through at least one wall of the furnace or at each of the corners, or roof mounted, depending upon the designs of the manufacturer. The burners are at least positioned so that combustion occurs at or near the center of the furnace interior so that the heat is more evenly spread.
The oil fuel is atomized by each gun and enters the furnace as a spray. There it is initially ignited by an ignitor probe which provides a short succession of electric discharges from its tip to cause initial combustion of the oil which thereafter continues as the oil is fed. In addition to the air which may be used to atomize the oil, other air is supplied through an air or wind box and is circulated within a larger conduit through which the oil gun is centered. This air enters the furnace concentrically with the atomizer tip of the oil gun to provide a source of air for proper combustion. Additionally, other air can be fed into the furnace from sources other than that of the atomizer tip.
The air is intended to insure complete as well as controlled combustion of the oil. Controlled combustion means that the flame should begin at or near the atomizer tip and extend to the center of the furnace interior in a large, bushy shape. When the combustion is not properly controlled, the flame may not begin until some distance from the tip and then it may burn with a narrow shape appearing more as a jet or torch. When this occurs, some quantity of the fuel is not combusted and it will either fall to the furnace floor or be carried through the furnace and become deposited on various heat transfer surfaces. The latter creates the potential for catastrophic air heater fires and the like. As to the combusted quantity, it may provide a flame beyond the center of the furnace which provides uneven heating and in extreme occasions it could focus on several of the tubes on the far wall which can lead to premature failure. In addition, for a specified heat input it is known that a narrow, pencil-like flame cannot provide the same amount of energy as a large bushy flame.
To overcome many of these deficiencies in flame control, multiple burner assemblies are provided as previously noted. Also, the supply of air, which is fed at controllable rates, is adjusted to provide more or less quantity within the furnace to bring the flame back to the atomizer tip and also to spread out its shape. Fans provide the combustion air and it is the circulation of air around the oil gun that is critical for proper flame development and stability. Existing burner assemblies have used various combinations of holes and air swirling devices in an attempt to create a structured turbulence that encompasses the oil spray and penetrates it to provide sufficient air at each oil particle in the expectation that complete and maximum combustion will occur.
Despite the years that burner assemblies have been employed and the many design variations, flame adjustment or control can take much time or fuel is wasted and in some instances, maximum combustion efficiency is never obtained. More complex assemblies may increase selective combustion efficiency components but these are more labor intensive and require longer down time of the furnace when work is required on the oil gun which must be periodically removed, disassembled and cleaned or replaced.